The binding of the items will be after they have been used in 1 battle... so you can try them on to see what they look like, but if you or your mercs take them to battle they become theirs for good... (only shops would buy them back), this is a must if we are to have viable game economy.
The binding on pick up is absolutely necessary for the special dungeons (those that are like the Dead man's crack), because they will present you with very unique monsters, which if you could sell the items will flood the market and make the items worthless...
So for selling only crafters will be able to sell rare+ items, plus the much more rare chance to meet special monster in the open, or get lucky and get special item from a normal monsters. (it is possible) And of course there is a possibility to buy an item from the stores, that you feel is with great stats and try to sell it through the auction.
Also we will think how we can make it, so if a party enters the multistage dungeons, all members would be able to use the dropped items. (still no selling)
Anyhow crafting will be important, so don't underestimate it.